The rapidly increasing sensitivity of mass spectrometers does not automatically solve the problem of finding low-abundance components in the forest of chemical noise. Various separation techniques, such as liquid chromatography (LC), mobility, or field asymmetric waveform ion mobility spectrometry (FAIMS), used in front of a mass analyzer can reduce chemical noise. However, in complex mixtures, components present at concentrations below 10-8 M can still be difficult to detect.
For example when mixtures of peptides or intact proteins are subjected to electrospray ionization (ESI), the resulting mass spectra are heavily convoluted These compounds form many multiply charged analogues (e.g., +2 to +20) that can be compacted into only a small portion of the m/z scale, quite often the same m/z space as chemical noise ions. This makes analysis and elucidation of individual species quite difficult.
Before one or more embodiments of the invention are described in detail, one skilled in the art will appreciate that the invention is not limited in its application to the details of construction, the arrangements of components, and the arrangement of steps set forth in the following detailed description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.